1. Field of the Invention
The present invention relates generally to centrifugal superchargers for providing increased airflow to an engine. More particularly, the present invention concerns a gear driven supercharger provided with an impeller shaft that dampens noise created by the transmission and thereby prevents the noise from being amplified by the impeller.
2. Discussion of Prior Art
A centrifugal supercharger traditionally has a transmission that drivingly connects the impeller to the power source (e.g., a belt drive of the engine). Although supercharger transmissions have been variously constructed, gear-type transmissions are most preferred because of their high load capacities and durability.
However, superchargers using a gear drive are often considered loud as compared to, for example, a supercharger using a belt drive. Those ordinarily skilled in the art will appreciate that the noise (typically a high-pitched shrill) generated by a gear driven supercharger is, in some conditions, greater than that generated by the engine. In fact, this problem is often one of the most common customer complaints associated with gear driven centrifugal superchargers.
Responsive to these and other problems, an important object of the present invention is to provide a supercharger that is capable of providing the desired horsepower increases. It is also an important object of the present invention to provide a supercharger that has the same durability and high load capacity as conventional superchargers but generates relatively less noise. In this regard, an important object of the present invention is to provide a low-noise supercharger that is capable of generating the desired horsepower increases. Yet another important object of the present invention is to provide a supercharger having a simple and inexpensive construction.
In accordance with these and other objects evident from the following description of the preferred embodiments, the present invention concerns a supercharger including a gear-type transmission having an impeller shaft that supports the impeller. The impeller shaft is fixed relative to one of the gears of the transmission, with at least a portion of either or both the shaft and the one gear being formed of cast iron. Such a construction causes dampening of sound waves propagating to the impeller, and amplification of transmission noise by the impeller is consequently reduced. The impeller shaft preferably has a minimum diameter that varies depending upon the desired horsepower gain provided by the supercharger.